1. Field of the Invention
The present invention is broadly concerned with fertilizer compositions and methods wherein the compositions include agriculturally valuable minerals, such as gypsum, members of the Kieserite Group, potassium magnesium sulfate, and elemental sulfur, together with an amount of a copolymer adjuvant or additive serving to significantly increase the availability of sulfate and other ions in soil, particularly during the early stages after application of the fertilizer compositions. More particularly, the invention is concerned with such fertilizer compositions and methods wherein the dried residue of an aqueous, very low pH copolymer dispersion (e.g., either a true solution or a mixture) coats the minerals and wherein the copolymer includes respective quantities of maleic and itaconic moieties.
2. Description of the Prior Art
Gypsum is a soft mineral compound formed of calcium sulfate (CaSO4), usually found in nature in the dihydrate form (CaSO4.2H2O). It is colorless to white with a silky, pearly, or waxy luster, and commonly has various colored impurities. Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. It may also be granular or quite compact. Gypsum has a number of commercial uses, and is well known as a fertilizer and soil conditioner. In the late 18th and early 19th centuries, Nova Scotia gypsum, often referred to as plaister, was a highly sought fertilizer for wheat fields. Gypsum is also used in ameliorating sodic soils. A significant advantage of gypsum is that it is relatively low in cost, while containing substantial quantities of nutrients; e.g., commercial gypsum grades normally contain about 22% Ca and 17% S.
When applied to soils, gypsum supplies crop-available forms of calcium and sulfate ions. However, owing to the very limited solubility of gypsum in water, positive fertilizing results or soil amendments may require a two or three year program of applications. Hence, although gypsum fertilizer use is well-recognized, the slow action of gypsum does not provide immediate help, either in the form of plant nutrition or soil remediation.
Kieserite is a form of magnesium sulfate (MgSO4.H2O) having a monoclinic crystalline system. There are a number of related minerals, known as the Kieserite Group, which includes other hydrated forms of magnesium sulfate, such as Epsomite (MgSO4.7H2O); the group also includes a relatively rare zinc-rich mineral Gunningite (Zn,Mn)(MgSO4.H2O). Comprehensive lists of Kieserite Group minerals may be found in Hammel (1939) Annales de Chimie, Paris: 11:247, and Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wylie and Sons, Inc. New York, 7th Edition, Revised and Enlarged, 1124 pp. 477, both of the foregoing being expressly incorporated in their entireties by reference herein. The Kieserite Group, because of the valuable plant nutrients therein, can be used as plant fertilizers.
Elemental sulfur is also commonly applied to soils in order to supply sulfate ion. However, elemental sulfur is converted to sulfate very slowly in normal soils, and thus the beneficial effects of sulfur applications may take several growing seasons to appear.
There is accordingly a need in the art for enhanced forms of fertilizer minerals which accelerate the availability of sulfate and other ions (e.g., Ca and Mg) in the soil.